The present invention relates to a spray nozzle grid configuration forming part of a misting system for humidifying air supplied to the inlet of a compressor for a turbine and particularly relates to a grid system for reducing obstruction to the flow of air in the inlet duct to the compressor while simultaneously affording substantially uniform distribution of the humidified air across the duct.
It is well known in gas turbine operation, that turbine output decreases in proportion to increases in ambient air temperature. However, gas turbine operators frequently encounter peak power generating requirements at elevated ambient temperatures, e.g., due to high air conditioning loads in major cities. It is economical and advantageous to generate additional power through auxiliary systems during those peak power demand periods. One auxiliary system for increasing power input is an inlet misting or fogging system which provides a direct spray of water into the inlet duct which, through an evaporative process, lowers the air temperature to the gas turbine and, hence, increases output.
Compressor inlet misting systems generally attempt to match the spray of water into the inlet duct to the evaporation potential of the air flowing to the gas turbine. Since ambient temperature conditions are variable, a variable spray of water and substantial turndown of the water spray are required. Existing misting systems employ multiple grids each having a substantial number of nozzles to spray the water into the inlet duct. However, as the water supply is turned down, the spray pattern in the inlet duct becomes much less uniform, resulting in less evaporation and more water carryover. Water carryover, e.g., large droplets of water, entering the compressor have the potential to erode the initial compressor stage. Additionally, the air flow is disrupted by the nozzles and ancillary piping in the inlet duct, resulting in reduced evaporation. These disruptions oftentimes disadvantageously form vortices in the flow downstream of the manifold tubes. Consequently, there is a need for a misting system which would provide a substantially uniform water spray into the gas turbine compressor at lower than full demand conditions with minimal obstruction to flow and generation of vortices which can disadvantageously cause droplet coalescence in the nozzle water spray plumes.